(a) Technical Field
The present invention relates to a system and method for controlling the operation of a fuel cell hybrid system. More particularly, it relates to a system and method for controlling the operation of a fuel cell hybrid system by using a fuel cell as a main power source and an energy storage device as an auxiliary power source, which can effectively avoid a low power and low efficiency region of a fuel cell during operation.
(b) Background Art
A typical fuel cell system within a hydrogen fuel cell vehicle includes a fuel cell stack for generating electricity by an electrochemical reaction of reactant gases, a hydrogen processing system for supplying hydrogen as a fuel to the fuel cell stack, an air processing system for supplying oxygen containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, and a thermal management system (TMS). The TMS is responsible for removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management function.
In the fuel cell system for a vehicle, when only the fuel cell is used as a power source for the vehicle, all loads that constitute the vehicle are powered by the fuel cell, and thus the performance of the fuel cell may deteriorate during operation where the efficiency of the fuel cell is low.
Consequently, when a sudden load is applied to the vehicle, the output voltage of the fuel cell suddenly drops, and thus sufficient power is not supplied to a drive motor, which may deteriorate the performance of the vehicle. Furthermore, a fuel cell has unidirectional output characteristics, and thus it is difficult to recover energy from the drive motor during braking of the vehicle. Accordingly, this also deteriorates the performance of the vehicle.
In an effort to overcome these drawbacks, the automotive industry has developed a fuel cell hybrid vehicle. The fuel cell hybrid vehicle is equipped with a suitable energy storage device such as a high voltage battery or a supercapacitor as an auxiliary power source for providing suitable power required for driving the drive motor and high voltage components in addition to the fuel cell as a main power source.
In this hybrid system, an idle stop mode, in which the power generation of the fuel cell is stopped in an idle state of the vehicle, is used. To avoid the low power region and thus improve the efficiency of the fuel cell system and increase the durability, a variety of methods for the avoidance operation of the low efficiency region have been proposed.
Typically, in a system where a fuel cell and a supercapacitor are directly connected together, the air supply is cut off to shut off the output of a fuel cell hybrid system. By doing so, the output of a fuel cell is directly controlled via the voltage of a bidirectional power converter.
More specifically, U.S. Pat. No. 7,196,492 discloses a method of implementing an idle stop mode of a fuel cell-supercapacitor hybrid system, in which the idle stop mode is determined based on the voltage of a main bus terminal and its change rate and the power generation of the fuel cell is suspended by the operation of a switch at an end of the fuel cell.
Moreover, U.S. Pat. No. 7,377,345 discloses an idle control system for a fuel cell vehicle equipped with a power converter. In this case, a power generation mode, where a fuel cell is operated at an optimal efficiency point, is performed when a vehicle load is small (i.e., during a normal load-following operation and a power generation stop mode where the power generation of the fuel cell is stopped is performed when the energy is high).
Furthermore, Korean Patent Publication No. 10-2010-0005768 also filed by the present applicant discloses an idle stop-start control method of a fuel cell hybrid vehicle including a fuel cell and a storage means, in which the air supply is cut off at a specific voltage such that the power generation of the fuel cell is automatically stopped without operation of a switch or power converter.
However, to date, neither a system nor a method for controlling the operation of a fuel cell hybrid system which can effectively avoid the low power and low efficiency region to of a fuel cell during operation has been effectively developed. This is true especially in relation to a more efficient idle stop-start control system and method.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.